Seals for automotive body applications (such as, windows, hoods, trunks and doors) and building applications (such as window glazing gaskets and weather strips) should be dimensional stable, provide low compression set, and offer outstanding sealing characteristics over a broad temperature range. Such seals must be capable of sealing out noise, wind and water, while providing long-term ultraviolet light resistance. At the same time the material used in the seal must offer the degree of flexibility required for the particular application. Window and door weather stripping for automobiles and trucks is a high volume application for such seals. However, seals offering essentially the same characteristics are also needed for sun roof seals, handle gaskets, window spacers, window guides, lock seals, windshield wiper pivot seals and in building applications such as window glazing gaskets and weather seals.
Rubbery blends of polyvinyl chloride (PVC) with a nitrile rubber (NBR) have sometimes been used in seals for automotive body applications. The nitrile rubber is included in such blends as a permanent modifier for the PVC which provides it with a higher degree of flexibility. However, the utilization of standard nitrile rubber in such blends typically results in only moderate compression set characteristics. It is very important for seals to have good compression set characteristics in most applications. For instance, improved resistance to water leaks and wind noise can be attained by utilizing a seal which has low compression set characteristics.
It is known from the teachings of UK Patent Application No. 9214969.9 that low compression set characteristics can be improved by utilizing a technique known as "dynamic vulcanization" via free radical generators, such as azo compounds or organic peroxides. However, this "dynamic vulcanization" technique suffers from the weakness that the azo compounds or organic peroxides required reduce the thermal stability of the polyvinylchloride resin and the ultraviolet light resistance of the nitrile rubber. There is also an increased risk of early crosslinking during processing which leads to scorching and reduced recyclability.
The automotive industry is currently moving toward cost reduction wherever it is possible without sacrificing quality. From a cost standpoint blends of nitrile rubber with polyvinylchloride are an attractive substitute for much more expensive materials which are widely used in automotive body seals. For this reason the development of a nitrile rubber which could be blended easily with polyvinylchloride to attain low compression set while maintaining dimensional stability, low temperature flexibility, and outstanding sealing characteristics would be warmly greeted.